FWM 318 Population analysis

1. FWM 318 Population analysis Jayeola, O.A

2. CHARACTERISTICS OF A POPULATION • Population studies in ecology deals with the study of numerical strength of plant and animal species in their natural environment. • In biological senses, a group of animal belonging to the same species and inhabiting same place can be refrred to as a population • A population is therefore characterised by features such as density, pressure, age distribution/structure, sex distribution/ratio, birth rate, death rate, reproductive/ productivity potential and growth. • Other characteristics of a typical biological population are sizes, biotic potential, environmental resisitance, carrying capacity, habitat resistance, biotic resistance, fecundity, migration, immigration, emigration, recruitment, open and close population sample and sampling, density dependent and density independent factors.

3. Population growth • Growth are affected by a wide variety of factors and thus maximum possible rate are rarely Achieved • Factors that are influencing the growth of a population can be grouped into 2 - Abiotic and Biotic factors. • Carrying capacity can be termed as the maximum number of animal or plants of a given species and quality that can in an ecosystem survive through through the least favourable conditions occurring within a stated time interval. Carrying capacity is not a stable property of a unit environment, but the result of ebb and flow of the interactions of organisms and their environments, therefore carrying capacity is not static but dynamic in nature, carrying capacity can thus be termed to be : • The number of animal of a given species that a habitat does support, determined by continuous observation over a period of years. • The upper limit of a growth above which no further increase can be sustained. • The number of individual that a habitat can maintained in a healthy vigorous condition.

4. Assumption on carrying capacity • Identification of key species or element which both plant and animal uses. • Finding the maximum level of use that the key species can tolerate • Determining the proportion of the diet that the key species make up for the animal or plant. • Determine the grazing capacity or utilization rates of the organisms. • Determining the attained utilization of other species when the key species is fully utilized by either animal.

5. Factor affecting productivity • Sex ratio i.e the ratio of male to female. When the females outnumbered males especially within the vertebrates it normally result in high productivity. • Gestation period – the period between fertilization of ovum to parturition or birth of the young animal is its gestation period. This varies from one animal species to the other, generally animals with shorter gestation period multiply faster and are capapble of carrying two or more pregnancy per year, e.g rat gestation is 27 days; porcupine =112 days; horse = 329 -345 days; Ground squirrel = 28 – 32 days; fox = 60 days and whale = 480 days. • Litter size or clutch size – the number of young per birth is a contributory factor to animal productivity • Pre-natal care – Adult animal that can give adequate parental care to its offspring in terms of provision of food, water, shelter and protection from predators. • Climatic factors – These include adequate rainfall, temperature, relative humidity etc. These factors create a good environment for breeding. It also stimulate vegetation growth that usually provide food and cover for animals and their newly born youngs whereas, adverse weather condition limit food source and will affect productivity. • Other factors such as disease and parasite infections, predation, age at puberty etc (discuss in class)

6. Population distribution • Clumped Species are common herds of animal or group of plants that have specific resource requirements and therefore gathered round the areas where those resources are found, e.g a herd of elephants, a school of dolphins or a stand of pines. • Uniform distributions usually occur where resources are thinly but evenly distributed or when individual of a species are antagonistic to each other, especially the large carnivores. • Random or Scattered dispersal pattern are the result of sufficient resources with no antagonisms.

7. Abiotic Factors Affecting Population Size. • Abiotic factors affecting a population are the non living elements of its environment. These include physical factors such as the amount sunlight, the wind speed and direction, water currents and seasonal variation in rainfall and temperatures along with factors such as soil pH and the chemical input into the environment by man. • Light has a more direct effect on the growth of plant population than on animals. Plants depends on light for photosynthesis and so population living in habitats with low light level have evolve strategies for coping with the situation. Animals are affected by light level in the ecosystem indirectly as a result of food plant distribution and seasonal light changes do affect reproductive pattern. • Temperatures of the environment affect the rate of enzyme-controlled reaction in plants and ectothermic animals. Therefore population grow rapidly in warmer regions. Reproductive behaviour of population is also affected by temperature. Many migratory birds undertake epic journey across the world to reach an area where the temperature is suitable for their pattern. • Wind adds to environmental stress, as it increases water and heat loss from the bodies of organisms. In areas of strong prevailing wind the numbers of species which can survive are reduced. Strong wind like hurricane can devastate populations; destroy woodland along with communities of plant and animal life. • Water current affect the type of organisms that can populate a region and numbers within those population. Current are most damaging to population when the strength increases suddenly especially when flooding occurs. Availability of water is not a problem in an aquatic medium but terrestrial environment’s inhabitants can be affected by water supply in the form of rainfall, rate of evaporation and loss through drainage in the soil. Water is needed for proper functioning of cells, or excretion and gametes transfer. Any situation of limited water supply will put stress on the populations. If the stress becomes severe, the organisms dies unless those who has designed coping strategies for stress like camel band cacti. • Oxygen is never deficient in air but can be in short supply in soil and water. Cold and fast flowing river allow sufficient oxygen to dissolve in it to support life while hot, still and stagnant water has limited supply of oxygen to help the population in it to survive. Similiarly, soil environment are usually aerated and allow oxygen for plant root respiration, but when the soil becomes waterlogged, the air spaces are filled with water and the plant root are deprived of oxygen. Soil structure and its mineral content is another factor that affect the size of population.

8. Biotic Factors • These are the living element of the environment of a plant or animal. They include : • Predation • Parasitism • Disease and competition

9. Basis for condition assessment of population • Age and sex composition or ratio of a population often are indices of habitat, health factor or of behavioural condition which directly affect the size in future. • Biologists uses sex and age information from a sample of animal population to estimate future decline or increase in number of that population and recommend as appropriate. • Many techniques are employed to determine age and sex in animals. Some are simple and are employed easily by almost anyone without special training, but for some species, sophisticated techniques are required. • The criteria for ideal sex and age determination techniques focus on the following: • Independence from irregular nutritional and physiological variations • Clear separations into age classes or year classes without subjective judgement • Suitability for living animals of all ages • Ease of application by semi skilled technicians. • Some standard techniques meet these criteria, but most do not. In most species, one or more of the ideal criteria must be compromised in order to obtain the information needed. The compromise usually depends on the degree of accuracy required and on the number of animal that can be obtained reasonably to get the information. • Sex and age ratio monitoring may not be allowed when working with rare or endangered species because the only accurate technique involves an unacceptable risk or sacrifice of too many individual. On the whole, the essence of monitoring normally determines the method to use. Also the implication of the result on decision making goes a long way to determine whether or not a more accurate method will be employed. • For some study such as social behaviour, errors in age-sex determination is unacceptable. • For species that take a year or more to attain breeding conditions, one usually determine their age in annual increment or year classes. • For those that breed atg less than one year of age and rarely exceed three years of age, year class accuracy is not necessary. It is sufficient to identify their age as either breeding or non breeding.

10. Population analysis • In wildlife studies, population analysis will provide information on : • The effect of predation • Hunting • Disease • Weather • New management practices and • Various other factors. • A multitude of techniques are available for estimating animal populations. But most have several limitations. Improved methods of analysis are needed.